In the aeronautical industry, in which disc brakes are widely used and are required to meet increasing levels of performance, technical research and development has mainly been directed to obtaining lighter weight, and higher admissible temperatures. Thus it has already been proposed that use be made of discs (rotating and/or stationary) of carbon, for example graphite, by virtue of the intrinsic advantages of such materials from the twin points of view of weight and remarkable admissible temperature. However, a major difficulty involved in the use of graphite is that the mechanical characteristics of this material are poor.
As regards anchoring the discs in rotation, it has already been proposed that either the graphite disc be adhered to a metal disc, or that the graphite disc be provided with metal rings acting as a band defining a scalloped configuration. However, these assemblies tend to be heavy, fragile and troublesome.
In the construction of U.S. Pat. No. 3,895,693, a rotor or stator for a disc brake comprises a mounting member provided with a friction lining formed at least in part by a plurality of graphite plates, each plate having two flat side faces and a peripheral surface which is perpendicular to the two flat faces, each plate being received in a recess in a side face of the mounting member, each recess having a flat bottom surface and being of a depth less than the thickness of the plate, the side wall of the recess being parallel to the peripheral surface of the plate and spaced from the peripheral surface of the plate by a distance greater than that necessary to permit thermal expansion and contraction of the mounting member and the plate and means for retaining each plate in its recess.
Thus, under the action of the braking couple, each graphite plate bears with its peripheral surface against the wall of its respective recess, that is to say, with a surface which is sufficiently large to transmit the braking force by a pressure sufficiently moderate to be compatible with the poor mechanical properties of the graphite, this arrangement causing the graphite to be worked exclusively in compression, in which mode the characteristics of the graphite are less weak.
The means for retaining each plate in its recess may comprise a countersunk rivet extending from the bottom of the recess and passing through the plate with a radial clearance greater than said spacing.
Alternatively, each graphite plate can be fixed in its recess by adhesion for example by gluing, by welding, by means of a pre-layer metallizing the graphite, or by an intermediate layer of a graphite having transition properties. The mounting members can be made of metal, for example steel, titanium, beryllium or alloys thereof, or of any material having suitable mechanical characteristics and density, including some varieties of graphite different from conventional graphite.
The graphite plates can be provided in recesses in the stator or the rotor of the brake, according to considerations of choice or convenience.
However, one of the important features of a brake is represented by the relation of the braking couple with respect to speed, or to the temperature of the parts of the brake which are liable to undergo a rise in temperature, or to time. According to the uses to which the brake is to be put, it is possible to seek to achieve constancy in the braking coupled for a given pressure, irrespective of the speed or temperature conditions, or it is possible to seek to achieve a relation between braking couple and speed or temperature.
For this purpose, U.S. Pat. No. 3,895,693 recommends using, in a heat sink brake, at least two kinds of friction pads, the qualities of which are different while being associated to achieve a given braking couple relation.
The stators can be provided with one kind of graphite pad and the rotors with another kind of graphite pad. It is also possible for the stators to be provided with two or more kinds of pads of different graphites and for the rotors to be provided with two or more kinds of pads of different graphites. Generally, it is also possible to associate, in the brake, friction pads made of graphite and friction pads made of another material such as, for example, steel, copper and alloys thereof.